1. Technical Field
The present disclosure relates to wireless networks and, more specifically, to a method and apparatus for association control in mobile wireless networks.
2. Discussion of the Related Art
A mobile wireless network is a set of spatially distributed base stations or access points (APs) that are each connected to a network, for example, a telephone network and/or the Internet. Each AP provides a coverage area within which it is able to communicate wirelessly to a mobile terminal and thus provide the mobile terminal with network access. As the mobile terminal travels beyond the coverage area of a first AP and into the coverage area of a second AP, network communication is handed off from the first AP to the second AP such that the mobile terminal may retain network access even when in motion.
Examples of mobile wireless networks include mobile telephone networks such as CDMA and GSM networks, networks based on IEEE 802.11 standards (WiFi), networks based on IEEE 802.16 standards (WiMAX), etc.
Handoff is performed as the mobile terminal travels beyond the coverage area of the AP currently providing network access. Specifically, handoff is performed before the signal received by the mobile terminal from the AP degrades below a point where network access is compromised. This point may be determined by monitoring the signal strength of the current AP and initiating a handoff when the signal strength of the current AP falls below a signal strength of an available AP.
Handoff of network access from one AP to another AP involves, among other concerns, determining which AP to handoff network access to. For example, the mobile terminal may be within the coverage area of multiple APs and there may be a selection of APs that may receive the handoff.
Conventionally, network access is handed off to the AP with the strongest signal. In such a situation, the mobile terminal may analyze the signal strength of each available AP and select a desired AP based on the strongest signal. Accordingly, as the mobile terminal leaves the coverage area of a first AP, network access may be handed off to another AP without a loss of network access.
However, frequent handoff of network access may be problematic for a mobile terminal. For example, handoffs may potentially cause interruption of data transfer across the network. When data transfer is involved in real-time communication service, such as a voice call, interruption of data transfer may be undesirable potentially leading to noticeable delays in communication. Additionally, interruption of data transfer may lead to unacceptable delays in interactive applications that rely upon network-based communication. Moreover, the process of handing off network access may be expensive in terms of battery drain and computational economy, both of which may be scarce in mobile terminals.
Approaches have been developed to minimize latency in handoffs. For example, S. Pack and Y. Choi, “Fast Inter-AP Handoff using Predictive Authentication Scheme in a Public Wireless LAN,” in proc. IEEE Networks Conference, Atlanta, Ga., August 2002; M. Shin, A. Mishra, and W. Arbaugh, “Improving the Latency of 802.11 Hand-offs using Neighbor Graphs,” in Proc. ACM MobiSys, Boston Mass., June 2004; A. Mishra, M. Shin, and W. Arbaugh, “Context Caching using Neighbor Graphs for Fast Handoffs in a Wireless Network,” in Proc. IEEE Infocom, Hong Kong, China, March 2004; and I. Ramani and S. Savage, “SyncScan: Practical Fast Handoff for 802.11 Infrastructure Networks,” in Proc. IEEE Infocom, Miami, Fla., March 2005; each of which are herein incorporated by reference. According to such approaches, channel scanning time and handoff latency may be minimized. However, such approaches have not been concerned with minimizing the number of handoffs, and accordingly, expense of battery drain and computational economy associated with handoffs is not minimized.